Rod-like molecules as single substances

There is no evidence for either a plastic or a condis phase of short w-alkanes. For instance, hexane exhibits a triclinic solid phase that melts 

Insertion of a carbonyl between two methylene groups transforms an n-alkane into an alkanone. Since the group volume and bond angle to neighboring carbon atoms of a carbonyl are only c. 15% and c, 4° larger, respectively, than those of a methylene [37-40], the intrinsic shapes and sizes of alkanes and alkanones with the same number of carbon atoms are very similar. On that basis, they should form similar solid phase structures differences may be attributable to the opposite 

Interestingly, a liquid crystalline phase is not formed upon heating or cooling another positional isomer of OB and BS, decyl dodecanoate (DD), in which the carboxy group is inserted near the middle of heneicosane [54]. Unlike OB and BS, DD does not flow under force and it exhibits only one (melting) transition by DSC when heated or cooled in the temperature range when the other two isomers are polymorphic. Its X-ray powder diffraction pattern indicates that DD 

Evidence for polymorphism and possible mesomorphic phases, but not for liquid crystallinity, has been found in studies on methyl, ethyl and propyl stearate (i.e. molecules in which the length of the acid part is maintained at IS carbon atoms and the length of the alcohol part is shorter than in BS) [43,52-55]. We hypothesize that enhanced rotation of an alkoxy group of moderate length in these carboxy-inserted alkanes (perhaps in combination with dipolar effects) includes sufficient disorder within molecular layers to transform the phases from condis to liquid crystals embedding the carboxy group near the middle of an alkane (as with DD) serves to attenuate alkyl chain motions near a layer interface and thus precludes the formation of liquid crystalline phases. These qualitative assertions can and should be tested experimentally using a wider variety of molecules than have been examined thus far. 

Within a layer of a KS gel, stearate molecules are hexagonally packed so that each layer resembles the organization of a smectic B liquid crystalline phase. Rubidium stearate can have gel phases in which stearate chains are packed either in a hexagonal (Gh) or in a rectangular 

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